A method of lining pipes is already known wherein a rigid plastics tube inserted in the pipe and having a smaller diameter than the pipe is inflated radially of the pipe by applying heat and pressure to the tube from inside and thereby line the pipe with the rigid plastics tube (see, for example, Unexamined Japanese Patent Publication No.88281/1983).
The rigid plastics tube lining is hard, therefore retains itself in the pipe lining state and is more excellent in quality than the soft tube lining which is bonded with an adhesive to the pipe for lining.
No particular problem is experienced in using the rigid plastics tube lining method for lining underground main pipes such as water supply pipes, gas pipes and sewer pipes, whereas a problem arises when a branch pipe portion extending from the main pipe to the surface of the ground is to be lined by this method. Since the branch pipe portion has one end connected to the main pipe, it is very difficult to carry out lining work through the opening of the other end which only is usable as a work opening.
In this case, the problem can be eliminated by excavating the ground and cutting off the branch pipe portion from the main pipe to form another work opening and line the pipe portion through both ends as in the usual work condition. However, this requires much labor and time for excavating the ground, cutting off the branch pipe portion and restoring the piping to the original state, hence an undesirable solution.